A large number of people with diabetes use some form of daily insulin therapy to maintain close control of their glucose levels. Currently, there are two principal modes of daily insulin therapy. The first mode includes syringes and insulin pens. These devices are simple to use and are relatively low in cost, but they require a needle stick at each injection, typically three to four times per day. The second mode includes infusion pump therapy, via an infusion cannula (i.e., an infusion needle or a flexible catheter), which requires an infusion pump. Infusion pumps, although more complex and expensive than syringes and pens, offer the advantages of continuous infusion of insulin, precision dosing, and programmable delivery schedules. This allows closer blood glucose control which can result in improved health outcomes.
The use of an infusion pump requires the use of a disposable component, typically referred to as an infusion set, tubing set or pump set, which conveys the insulin from a reservoir within the pump into the skin of the user. An infusion set typically consists of a pump connector, a length of tubing, and a hub or base from which an infusion needle or catheter extends. The base has an adhesive that retains the base on the skin surface during use. The base may be applied to the skin manually or with the aid of a manual or automatic insertion device. Often, the insertion device is a separate, stand-alone unit that the user is required to carry and provide.
There are many available types of infusion sets incorporating various types of infusion cannulas, including steel needle infusion sets and soft catheter sets. Soft catheter sets can be inserted into a patient manually with the aid of a steel introducer needle, which is later removed from the patient, leaving the soft catheter in place. Alternatively, a mechanized inserter can be used to insert the introducer needle and catheter, after which the introducer needle is removed. In either case, the introducer needle is completely removed from the infusion set before the infusion set is connected to the insulin pump.
Another type of insulin infusion device is a patch pump. Unlike a conventional infusion pump and infusion set combination, a patch pump is an integrated device that combines most or all of the fluid components (including the fluid reservoir and pumping mechanism) in a single housing which is adhesively attached to an infusion site, and does not require the use of a separate infusion (tubing) set. A patch pump adheres to the skin, contains insulin (or other medication), and delivers the insulin over a period of time via an integrated subcutaneous catheter. Some patch pumps communicate with a separate controller device wirelessly (as in one device sold under the brand name OmniPod®), while others are completely self-contained. These devices need to be reapplied on a frequent basis, such as every three days, when the reservoir is exhausted or as complications may otherwise occur.
FIG. 1A illustrates an infusion set 1 for use with an infusion cannula such as a catheter 14. As illustrated in FIG. 1A, the infusion set 1 comprises a fluid connector or hub 22 which is detachably attached to a base (10), a fluid tubing set 24 and a connector 26 which attaches to a pump (not shown). Line set 20 includes the hub 22 and the fluid tubing set 24 is attached to or detached from the base 10, as in FIGS. 1B and 1C.
FIG. 1B is a top view of the infusion set 1 with the hub 22 attached to the base 10. An adhesive pad 18 is attached to the base 10 and is configured to be attached to the skin of the user. FIG. 1C illustrates a view of the infusion set 1 when the line set 20 is detached from the base 10. The base 10 includes an infusion adapter 15 to which the catheter 14 is attached.
FIG. 1D is a cross-sectional view of the infusion set 1 and more clearly illustrates how the infusate is pumped into the catheter 14, which is preferably made of a soft plastic material. The hub 22 of the line set 20 includes a hub port 29 that receives the fluid tubing set 24. The hub 22 includes a flow cannula 23 and a fluid channel 28 positioned between the fluid tubing set 24 and the open tip 231 of the flow cannula 23. The base 10 includes a main base portion 12 to which the catheter 14 is secured. A pre-slit septum 16 encloses the adapter 15, when the hub 22 is detached from the infusion base 10, as illustrated in FIGS. 1C and 1E. When the hub 22 is attached to the base 10, the flow cannula 24 penetrates the pre-slit septum 16 so that the fluid channel 28 is in fluid communication with the catheter 14. This allows infusate from the pump (not shown) to flow from the fluid tubing set 24 into the fluid channel 28, and into the catheter 14, and the infusate exits the distal opening 141 of the catheter 14 into the patient.
Infusion cannulas for use in infusion sets and/or patch pumps are manufactured of either rigid material, such as stainless steel, or soft plastic materials, such as fluorinated polymers, including TEFLON® polymer. Infusion cannulas may be subject to kinking and occlusion.
A catheter can kink during or after insertion into a patient when the catheter tube becomes bent due to various causes, resulting in a restricted flow of infusate exiting the catheter. Kinking can be considered to be the cessation of flow through a catheter due to mechanical causes, such as bending of the catheter, sliding back or folding of the catheter on the introducer needle during insertion.
The restricted flow of the catheter can be caused by kinking and by other causes. In general, occlusion is the blockage or cessation of flow due to biological, pharmacological or mechanical causes, including kinking, and these failures typically occur during the use cycle.
Rigid catheters, such as stainless steel cannulas, may have a sharp tip, which is used to pierce the skin, similar to an introducer needle in a conventional inserter. Rigid catheters are recommended for individuals who experience a high incidence of kinking. However, such products are not recommended for use beyond two days, because they can reduce site patency, due to tissue irritation.
On the other hand, soft plastic catheters, such as the catheter 14 illustrated in FIG. 1D, may be prone to kink or occlude with normal wear, while rigid catheters (not shown) are often found to be uncomfortable to the user, since they tend to move around within the tissue.
In infusion devices, it is highly desirable to minimize the risks of catheter occlusion, kinking and other complications, while maintaining a degree of comfort to the user. Kinking and occlusion are described in detail below.
As noted above, kinking is considered to be the cessation of flow through a catheter due to mechanical causes. This failure mode can be the result of insufficient interference between the inner diameter of the catheter and the outer diameter of the introducer needle during insertion. In addition, kinking can occur if a blunt distal end of the catheter allows excess force to be transmitted to the catheter as the catheter initially penetrates the outer surface of the skin. Similarly, excessive bounce or vibration in the insertion mechanization may result in excessive force being transmitted to the catheter.
Kinking can also occur during the infusion or use cycle. A typical cause of this failure is the placement of the catheter into tissue which undergoes significant movement during physical activity, which weakens the structure of the catheter, making the catheter less likely to resist mechanical forces that may bend or twist the catheter. Damage that causes deformation of the catheter may also contribute to kinking.
There are many advantages to flexible catheters, including ease of insertion into a patient, user comfort, and reasonable cost. However, there can also be some disadvantages. Flexible catheters are generally more susceptible to kinking than non-flexible catheters. The material used in most flexible catheters is a polymer, such as TEFLON® polymer. Such material provides flexibility to the catheter. However, the flexible nature of such catheters contributes to kinking because the walls of such catheters are not rigid and are therefore susceptible to deformation due to movement of the catheter and/or the patient.
Accordingly, a need exists for an improved catheter design and construction that will improve the functionality of the catheter while minimizing the disadvantages noted above. More specifically, a need exists to improve the design and construction of a flexible catheter that maintains its flexible characteristics without the negative aspects of the flexible design that contribute to kinking.